Multi-wavelength transmittance spectra of bacteria in water contain lots of information on their characteristics such as structure, constituent and concentration, and the effective extraction of the information is the foundation of rapid identification and detection of bacteria. The transmittance spectrum of Escherichia coli is recorded with a ultraviolet-visible spectrophotometer. According to Mie scattering theory and absorption and scattering properties, bacterial multi-wavelength transmittance spectrum analytical model in 240-900 nm band is constructed. Based on the model, the spectrum in the range of 250-750 nm is analyzed, the related parameters such as volume, diameter, structure and concentration of Escherichia coli cells are obtained, and these parameters are then compared with the literature data or experimental data. It is shown that the proposed multi-wavelength transmission spectrum model can accurately characterize the spectral features of bacteria in water, and the model can provide important parameters for the rapid analysis and detection of bacteria in water.